Liquid crystalline epoxy resins

ABSTRACT

Liquid crystalline epoxy compounds, compositions including the compounds, and methods of using the compositions are disclosed. In one aspect, an epoxy compound may have a melting point that is less than 140° C. and may be liquid crystalline at a temperature greater than 150° C.

BACKGROUND

1. Field

An embodiment of the invention relates to a liquid crystalline epoxyresin.

2. Background Information

Various liquid crystalline epoxy resins, their properties, and theiruses are known in the arts. Examples of liquid crystalline epoxy resinsinclude epoxylated trans-stilbenediol and epoxylated3,3,5,5-tetramethyltrans-stilbenediol. Such liquid crystalline epoxyresins generally exhibit unique properties, such as low viscosity flow.The low viscosity flow may allow the resins to be more easily flowedinto narrow or confined spaces. However, such liquid crystalline epoxyresins also generally tend to have relatively high melting points. Thehigh melting points may potentially limit the use of the resins.

DETAILED DESCRIPTION

In the following description, numerous specific details are set forth.However, it is understood that embodiments of the invention may bepracticed without these specific details. In other instances, well-knownstructures and techniques have not been shown in detail in order not toobscure the understanding of this description.

I. Liquid Crystalline Epoxy Monomer Compounds

An exemplary liquid crystalline epoxy monomer compound, according to oneembodiment of the invention, may have the following chemical formula:

In this formula, Ar may include a liquid crystalline moiety, X¹ and X²may, independently of one another, be connecting groups selected fromoxygen, carbonyl, carboxyl (O═C—O), oxycarbonyl (O—C═O), and amine, andn¹ and n² may, independently of one another, be a number selected from 2to 20.

First, let's discuss the liquid crystalline moiety, Ar. The term liquidcrystalline moiety generally refers to a shaped moiety, such as arod-shaped moiety or a disc-shaped moiety, which is sufficient to atleast promote orientational order of the compounds in the liquid phase.In one aspect, as in a nematic ordering of compounds, the mean directionof the compounds may be parallel or anti-parallel to an axis known asthe director. The ordered fluid phase may provide anisotropy of physicalproperties (e.g., the properties vary with direction).

Numerous liquid crystalline moieties known in the arts may be employed.Suitable liquid crystalline moieties (Ar) include, but are not limitedto, trans-stilbenediyl, triphenyl,1,4-bis(phenoxycarbonyl)-cyclohexdiyl, and diphenyl1,4-cyclohexane-dicarboxylate. Many other suitable liquid crystallinemoieties are known in the arts. The liquid crystalline moieties may tendto include aryl groups, such as one or more phenyl groups, althoughthere is no requirement that the entire group be aromatic or aryl. Thesemoieties each have shapes or configurations that at least tend topromote alignment or orientational ordering of the compounds. Onepotential advantage of the compound is that known liquid crystallinemoieties may optionally be employed. These moieties are oftencommercially available and their properties tend to be wellcharacterized.

The liquid crystalline moiety (Ar) is connected on a first side thereofto X¹ and on a second side thereof to X². X¹ and X² may, independentlyof one another, represent oxygen, carbonyl, carboxyl, oxycarbonyl, oramine. X¹ connects the liquid crystalline moiety to a first aliphaticmoiety, —(CH₂)_(n1)-, and X² connects the liquid crystalline moiety to asecond aliphatic moiety, —(CH₂)_(n2)-.

Now, let's discuss the aliphatic moieties in greater detail. Thealiphatic moieties generally represent flexible hydrocarbon chains. Thelengths of the chains are determined by n¹ and n², which represent thenumber of carbon atoms in the first and second aliphatic moieties,respectively. In one embodiment of the invention, n¹ and n² may,independently of one another, be a number selected from 2 to 20. Whenthe number of carbon atoms exceeds about 20, the compounds may tend tohave high viscosities, and the temperature range between the meltingpoint and the isotropic point, or the temperature where propertiesbecome the same in all directions, may tend to diminish. Often, themelting point may tend to increase and the isotropic point may tend todecrease. This may tend to limit the range over which the compounds areliquid crystalline. In an embodiment where lower viscosities areappropriate, and where it is appropriate to maintain more liquidcrystalline character, it may be appropriate for n¹ and n² to be lessthan about 15. For example, in various alternate embodiments of theinvention, n¹ and n² may, independently of one another, be a number from2 to 10, 2 to 6, or 3 to 5.

Now, the flexible hydrocarbon chains may tend to disrupt the liquidcrystalline characteristics of the compound. The amount of disruption ofthe liquid crystalline characteristics generally increases withincreasing length of the chains (i.e., greater n¹ and n²). Without beingbound by theory, it is believed that a long and flexible hydrocarbonchain may reduce the capability of the compounds to order.

In one aspect, the ability to tailor the lengths of the chains may allowmodifying or tailoring certain characteristics of the compound thatdepend upon the liquid crystalline character. One such characteristic isthe melting point temperature of the compound. As previously discussed,liquid crystalline epoxy resins tend to have relatively high meltingpoint temperatures. These high melting point temperatures maypotentially limit the uses and applications of the compounds. However,the ability to tailor the lengths of the chains may allow reducing themelting point to a desired extent or tailoring the melting pointtemperature of the compound. Typically, disruption of the liquidcrystalline characteristics of the compound corresponds to a reductionin the melting point temperature of the compound.

In one embodiment of the invention, n¹ and n² may be selected to besufficiently great to reduce a melting point of the compound to adesired extent by reducing the liquid crystalline character of thecompound due to the liquid crystalline moiety. Likewise, n¹ and n² maybe selected to be sufficiently small to retain at least some liquidcrystalline character of the compound in order to exploit low viscosityand other unique properties of liquid crystals. This ability to reducethe melting point temperature, while retaining at least some liquidcrystalline character, may allow the low viscosity flow and other uniquecharacteristics of the liquid crystalline epoxy resin compounds to beexploited in temperature-limited environments and applications.

One such temperature-limited application is the transfer molding ofmicroelectronic devices during packaging. Much of the currentlyavailable transfer molding equipment used in the microelectronic devicepackaging industry is designed to perform transfer molding at atemperature between about 150 to 180° C., often at about 165° C. Theequipment is often poorly suited for performing transfer molding atsignificantly greater temperatures. For example, the heating elements ofthe mold cavities, as well as other components, may be under-designedfor such operation. The equipment may tend to perform poorly if utilizedon many liquid crystalline epoxy resins, such as epoxylatedtrans-stilbenediol, which has a melting point temperature of about 210°C. Additionally, performing transfer molding at high temperaturesapproaching the softening point of solders may tend to promote soldersweep failures and decreased manufacturing yields.

In one embodiment of the invention, in which the compounds are employedin molding microelectronic devices, n¹ and n² may be sufficient,depending upon the particular liquid crystalline moiety, to achieve amelting point temperature that is below about 140° C. (for examplebetween about 90 to 140° C.), while retaining liquid crystallinity attemperatures of from about 150 to 180° C. Often, the melting point andisotropic points may be reduced by commensurate amounts, so that thedifference between these two temperatures, which generally defines aprocessing window over which liquid crystalline behavior may beexploited, may remain about the same. Due in part to the wide variety ofliquid crystalline moieties, and the wide variety of potentiallydifferent combinations of X¹ and X² that may potentially be employed,placing a single precise circumference on n¹ and n² may tend to bedifficult. However, often for highly liquid crystalline moieties, n¹+n²may tend to be less than about 10, and for lesser liquid crystallinemoieties, n¹+n² may tend to be less than about 6.

To illustrate certain concepts, particular straight-chain,un-substituted, aliphatic moieties have been employed, although otherembodiments of the invention are not so limited. For one thing, theillustrated aliphatic moieties include only carbon and hydrogen,although this is not required. In another embodiment of the invention,one or more halogens, such as fluorine, chlorine, bromine, or iodine,may optionally be substituted one-for-one with hydrogen. Additionally,the use of a straight-chain aliphatic moiety is not required. In anotherembodiment of the invention, a limited number of short-chain methyl orethyl branches may optionally be included. Generally, depending upon theparticular liquid crystalline moiety, and depending upon the symmetry ofthe branches, it may be appropriate to avoid using an overly largenumber of branches, and/or overly large branches, which may tend tocompromise the liquid crystalline capability of the compound. Dependingupon the particular compound, even one or two t-butyl branches may tendto significantly disrupt liquid crystallinity.

Referring again to chemical formula (II), a first terminal epoxy groupis attached to the first aliphatic moiety, —(CH₂)_(n1)-, and a secondterminal epoxy group is attached to the second aliphatic moiety,—(CH₂)_(n2)-. In one aspect, the epoxy groups may be polymerized, forexample with a curing agent. Accordingly, another embodiment of theinvention may relate to a dimer, trimer, or other polymeric compoundincluding a plurality of polymerized epoxy monomers.

Another exemplary liquid crystalline epoxy monomer compound, accordingto an embodiment of the invention, may have the following chemicalformula:

In this formula, Ar may include a liquid crystalline moiety, X¹ and X²may, independently of one another, be selected from oxygen, carbonyl,carboxyl, oxycarbonyl, and amine, Y¹ and Y² may, independently of oneanother, be selected from oxygen, carbonyl, carboxyl, oxycarbonyl, andamine, and n¹ and n² may, independently of one another, be numbersselected from 2 to 20.

The compound of formula (II) includes an internal moiety with thefollowing chemical formula:—(CH₂)n¹-X¹—Ar—X²—(CH₂)n²-   (III)This internal moiety is similar to the internal moiety described inconnection with the compound of chemical formula (I). In general, theinternal moiety may have the same characteristics as previouslydescribed. In order to avoid obscuring the description, generally thediscussion below will focus primarily on the different and/or additionalaspects of the compound.

Referring again to chemical formula (II), a first aliphatic moiety,—(CH₂)n¹-, is bonded to Y¹ and a second aliphatic moiety, —(CH₂)n²-, isbonded to Y². The Y¹ and Y² may, independently of one another, beconnecting groups selected from oxygen, carbonyl, carboxyl, oxycarbonyl,and amine. Y¹ is connected by way of a —(CH₂)— group a first terminalepoxy group, and Y² is connected by way of a —(CH₂)— group to a secondterminal epoxy group.

As discussed above, one potential advantage of using the compounds offormulas (I) and (II) is that known liquid crystalline moieties, such astrans-stilbenediyl, for example, may be employed. This may offeradvantages, inasmuch as these moieties tend to be available and wellcharacterized. However, as demonstrated below, other embodiments arealso contemplated.

Another exemplary liquid crystalline monomer compound, according to anembodiment of the invention, may have the following chemical formula:

In the formula, X may be selected from acetylene, vinyl, butadiene, anaryl group, and an alicyclic group, each R¹ may be independentlyselected from hydrogen, halogen, and C₁₋₃ alkyl groups optionallysubstituted with halogen, and each R² may be independently selected froma C₂₋₁₀ epoxy.

The X-group is located in an intermediate portion of the compound. Inone embodiment of the invention, X may be selected from acetylene,vinyl, butadiene, a C₆₋₁₀ aryl group, and a C₅₋₁₀ alicyclic group.Suitable C₆₋₁₀ aryl groups include, but are not limited to, phenyl andnapthyl. In another embodiment, larger aryl groups, such as polyaromatichydrocarbons, may also potentially be employed. Suitable C₅₋₁₀ alicyclicgroups include, but are not limited to, monocyclic rings, and polycyclicrings. Exemplary monocyclic rings include, but are not limited to,cyclopentyl, cyclohexyl, cycloheptyl, and cyclooctyl. Exemplarypolycyclic rings, also known as cages, include, but are not limited to,tricyclo[3,3,1,1^(3,7)]decane (also known as adamantane),bicyclo[2.2.1]heptane (also known as norborane), bicyclo[4.3.0]nonane,bicyclo[3.2.1]octane, and bicyclo[2.2.2]octane. In another embodiment,larger alicyclic cages having up to about thirty carbon atoms may alsopotentially be employed.

The X-group is connected with a first aryl group via a first esterlinkage at a first side thereof, and connected with a second aryl groupvia a second ester linkage at a second side thereof. In the illustratedcompound, the X-group is bonded to the carbonyl (C═O) groups of theester linkages. In an alternate embodiment of the invention, the arylgroups may be bonded to the carbonyl groups of the ester linkages (seechemical formula VI).

The aryl groups, which in the illustrated compound include phenylgroups, tend to have rigid, planar configurations that may tend topromote orientational ordering of the compounds and liquidcrystallinity. Often, the two aryl groups may give the compound agenerally rod-like shape. In contrast, the ester linkages tend to beflexible and tend to bend and rotate. Such flexibility may tend toslightly reduce the liquid-crystalline characteristics of the compound,and correspondingly reduce the melting point and isotropic pointtemperatures of the compound.

Further, each of the aryl groups is substituted with four R¹ groups.Each R¹ may be independently selected from hydrogen, halogen, and C₁₋₃alkyl groups optionally substituted with halogen. In one aspect,depending upon the liquid crystallinity provided by the aryl groups,depending upon the X-group, and depending upon the desired meltingpoint, one or more of the R¹ groups may be selected to be non-hydrogengroups, such as halogens or C₁₋₃ alkyl groups. This may tend to disruptthe liquid crystallinity of the compound and reduce the melting pointand isotropic transition temperatures. In general, the use of a largenumber of C₁₋₃ alkyl groups, or the use of several C₃ alkyl groups, maytend to significantly disrupt the liquid crystallinity.

Referring again to chemical formula (IV), a first and a second R²-groupsare connected to the first and second aryl groups, respectively. In theillustrated compound, they are connected in para-positions relative tothe ester linkages, although this is not required. In anotherembodiment, the R²-groups may be connected in potentially differentmeta- or ortho-positions. The meta- and ortho-positions may tend toreduce the rod-like character of the compound, and temper the liquidcrystallinity.

Each R²-group may be independently selected from a C₂₋₁₀ or C₂₋₅ epoxygroup. Suitable epoxy groups include straight-chain epoxy groups andbranched-chain epoxy groups. Suitable C₂₋₅ epoxy groups include, but arenot limited to, 1,2-epoxyethane, glycidyloxy, 3,4-epoxypropyl, and thelike. Diepoxy compounds, such as 1,2,3,4-diepoxybutane, are alsosuitable. Suitable C₂₋₁₀ epoxy groups include these aforementioned epoxygroups as well as those including longer, straight or branched alkylchains, such as 1,2-epoxydecane. In general, a longer and more flexibleepoxy group may tend to reduce the liquid crystalline character of thecompound, and may tend to reduce the melting point and isotropictransition temperatures. In one aspect, the length of the epoxy groupsmay have a similar affect as the length of the hydrocarbon chains inchemical formula (I).

Now, let's discuss the X-group in greater detail. The different X-groupsmay affect the melting point temperatures and anisotropic-to-isotropictransition temperatures of the compounds. Table 1 lists data by othersincluding melting point temperatures and anisotropic-to-isotropictransition temperatures for a class of non-epoxy compounds having thedifferent X-groups listed and having the following chemical formula:

TABLE 1 Melting Point Isotropic Transition X-Group (° C.) (° C.) Phenyl188 235 Norboryl 113 226 Cyclohexyl 110 213 Vinyl 108 140 Acetylene 92100

As shown, acetylene may reduce the melting point and isotropictransition temperatures more than vinyl, vinyl may reduce thetemperatures more than cyclohexyl, cyclohexyl may reduce thetemperatures more than norboryl, and norboryl may reduce thetemperatures more than phenyl. Without wishing to be bound by theory, itis believed that an aryl group like phenyl tends to more rigid and lessflexible than an alicyclic group, like norboryl, or cyclohexyl.

Viewed from one perspective, the data in Table 1 gives estimates of themelting point and isotropic transition temperatures for compounds of thechemical formulas (IV) (and also (VI)), for different X-groups, when R¹are all hydrogen, and when the R² include about four carbons each.However, as disclosed in the chemical formula, all of the R¹ need not behydrogen. Rather, the R¹ may be selected from hydrogen, halogen, or C₁₋₃alkyl groups optionally substituted with halogen.

In one embodiment of the invention, the set of R¹-groups may be selectedto adjust or tailor the melting point and isotropic transitiontemperatures. In general, substituting a halogen or C₁₋₃ alkyl groupoptionally substituted with halogen for hydrogen may tend to reduce themelting point and isotropic transition temperatures. Typically, a C₃alkyl group may reduce the temperatures more than a C₂ alkyl group, anda C₂ alkyl group may reduce the temperatures more than a C₁ alkyl group.For halogens, the reduction may depend on the size of the halogen.

Based on the data in Table 1, a relatively greater disruption of liquidcrystallinity may be appropriate for a compound including phenyl, thanfor a compound including cyclohexane, for example. The greaterdisruption may generally be achieved by including relatively morehalogens or C₁₋₃ alkyl group optionally substituted with halogen inplace of hydrogen. The greater disruption may also generally be achievedby using larger C₁₋₃ alkyl groups, such as C₂₋₃ alkyl groups.

In one particular embodiment of the invention, the set of R¹-groups maybe selected to reduce the melting point temperature of the liquidcrystalline epoxy compound to below about 140° C., while retainingliquid crystallinity at a temperature greater than about 150° C. Tofurther illustrate, based on the data in Table 1, several hypotheticalcompounds that may tend to have these properties given as the followingexamples.

As one example, consider a compound in which X is cyclohexane, each R²is selected from a straight-chain C₂₋₆ epoxy, and either: each R¹ ishydrogen; one or two of the R¹ may be potentially different halogens; orone of the R¹ may be methyl or ethyl.

As another example, consider a compound in which X is norbomyl, each R²is selected from a straight-chain C₂₋₆ epoxy, and either: each R¹ ishydrogen; one or two of the R¹ may be potentially different halogens;one or two of the R¹ may be methyl or ethyl; or one of the R¹ may bepropyl.

As yet another example, consider a compound in which X is phenyl, eachR² is selected from a straight-chain C₂₋₆ epoxy, and either: two of theR¹ are C₃ alkyl; or about six of the R¹ may be C₁ alkyl.

Another exemplary liquid crystalline epoxy monomer compound, accordingto another embodiment of the invention, may have the following chemicalformula:

As shown, this formula is similar to that of chemical formula (IV), withthe exception that the aryl groups, rather than the X-group, are bondedto the carbonyl groups (C═O) of the ester linkages. Otherwise, theX-group, ester linkages, phenyl groups, R¹-groups, and R²-groups may beas previously described.II. Epoxy Molding Compositions

In one embodiment of the invention, one or more of the liquidcrystalline epoxy monomer compounds disclosed herein may be included inan epoxy molding composition. Other ingredients that may optionally beincluded in the epoxy molding composition include, but are not limitedto, one or more curing agents, curing accelerators, curing inhibitors,and fillers.

Suitable curing agents include, but are not limited to, polyphenol typeand polynaphthol type novolac resins; polyaralkylphenol resins andpolyaralkylnaphthol resins; alicyclic hydrocarbon-containing polyphenolresins and polynaphthol resins; cyclic phenols such as callixallene orthe like; dihydric phenol compounds such as Bisphenol A, Bisphenol F,hydroquinone, resorcin, dihydroxynaphthalene,bis(4-hydroxyphenyl)ethane, bis(4-hydroxyphenyl)propane, and the like;halogenated bisphenols such as Tetrabromobisphenol A and the like;polyhydric phenols; polycarboxylic acids such as maleic acid, phthalicacid, nasic acid, methyl-tetrahydrophthalic acid, methyl-nasic acid andthe like, and anhydrides thereof; polyanhydrides, polyamine compoundssuch as diaminodiphenylmethane, diaminodiphenyl sulfone, diaminodiphenylether, phenylenediamine, diaminodicyclohexylmethane, xylylene diamine,tolylene diamine, diaminocyclohexane, dichlorodiaminodiphenylmethane(including isomers), ethylene diamine, hexamethylenediamine and thelike; and active hydrogen-containing compounds which can react withepoxy group such as dicyandiamide, tetramethylguanidine and the like. Inone aspect, the molar ratio of curing agent to epoxy monomer may be fromabout 0.5 to 1.5 or from 0.7 to 1.2.

Typically, a curing accelerator, such as a catalyst, may be included inthe composition. Suitable curing accelerators include, but are notlimited to, organic phosphine compounds such as triphenylphosphine,tri-4-methylphenylphosphine, tri-4-methoxyphenylphosphine,tributylphosphine, trioctylphosphine, tri-2-cyanoethyl-phosphine and thelike; organic phosphonium salts such as tetraphenylphosphoniumtetraphenylborate and the like; tertiary amines such as tributylamine,triethylamine, 1,8-diazabicyclo(5,4,0)undecene-7, triamylamine and thelike; quaternary ammonium salts such as benzyltrimethylammoniumchloride, benzyltrimethylammonium hydroxide, triethylammoniumtetraphenylborate and the like; imidazoles; boron trifluoride complexes;transition metal acetylacetonates; and radical initiators such asbenzoyl peroxide, di-t-butyl peroxide, dicumyl peroxide, lauroylperoxide, acetyl peroxide, methyl ethyl ketone peroxide, cyclohexanoneperoxide, t-butyl hydroperoxide, azobisisobutyronitrile and the like.Typically, the molar ratio of curing agent to epoxy monomer may be fromabout 0.001:1 to 0.1:1.

If desired, a curing inhibitor may optionally be used in combinationwith the curing accelerator to adjust the rate of polymerization.Suitable curing inhibitors include, but are not limited to, phenolcompounds such as 2,6-di-t-butyl-4-methylphenol,2,2′-methylenebis(4-ethyl-6-t-butylphenol),4,4′-methylenebis(2,6-di-t-butylphenol),4,4′-thiobis(3-methyl-6-t-butylphenol), hydroquinone monomethyl etherand the like; polyhydric phenol compounds such as hydroquinone,catechol, p-t-butylcatechol, 2,5-di-t-butylhydroquinone,methylhydroquinone, t-butylhydroquinone, pyrogallol and the like;phenothiazine compounds such as phenothiazine, benzophenothiazine,acetamidophenothiazine and the like; and N-nitrosamine compounds such asN-nitrosodiphenylamine, N-nitrosodimethylamine and the like. Typically,the molar ratio of curing inhibitor to epoxy monomer may be from about0.001:1 to 0.05:1.

Often, particularly in microelectronic applications, it may beappropriate to include filler in the composition. The filler may beincluded, for example, to modify a physical property of the composition.In the case of using the composition to encapsulate a microelectronicdevice, the filler may be included to modify a coefficient of thermalexpansion (CTE) of the composition so that it more closely approximatesor matches a CTE of a material of the microelectronic device. In oneaspect, the microelectronic device may include a silicon die, and thefiller may have a CTE matched to that of silicon, like that of silicon,or at least comparable to that of silicon. As used herein, a CTE of afiller is comparable to that of silicon if it is closer to silicon thanto an epoxy medium in which it is employed. This may help to allow thedevice and encapsulant to thermally expand and contract together. Thismay help to avoid potentially damaging mechanical stresses due tochanges in temperature. Suitable fillers that have CTE that arecomparable to that of silicon include, but are not limited to siliconparticles, silica particles, sand, quartz, silicon dioxide, clay, andthe like. In various aspects, the filler may be added in amounts of fromabout 50 to 95 wt %, or 75 to 95 wt %, based on the total weight of thecomposition.

If desired, in another aspect, the molding composition may optionallyinclude one or more surface-adhesion promoters, mold release agents,stress stabilizers, flame retardants, or colorants. Suitablesurface-adhesion promoters include, but are not limited to, varioussilane coupler compounds. An exemplary silane compound is3,4-epoxypropyl trimethoxy silane. Suitable mold release agents include,but are not limited to, natural waxes, synthetic waxes, paraffins,silicon oils, and the like. An exemplary mold release agent is carnaubawax.

Suitable stress stabilizers include, but are not limited to,polybutadiene, butadiene-acrylonitrile copolymer, silicone rubber,silicone oil, emulsified acrylate rubber particles, and otherelastomers. An exemplary stabilizer is epoxy terminated polybutadienerubber. Suitable flame retardants include, but are not limited to,antimony trioxide, phosphorus compounds, brominated compounds, and thelike. Exemplary flame retardant include brominated phenolic novolakresins and brominated epoxy resins. Suitable colorants include, but arenot limited to, carbon black, various dyes, and the like. For example,carbon black is often used in molding compositions, and green dyes areoften used in the epoxy compositions for dielectric substrates.

The epoxy compounds and one or more of the above-identified ingredientsmay be combined and mixed to form the compositions. In one aspect, theepoxy compound and the one or more other ingredients may be mixed usingone or more of a blender, kneader, mill, or other resin-mixing device.After mixing, the mixed material may optionally be grinded to anappropriate particle size and, if desired, pressed or otherwise formedinto pellets or other shaped solids.

III. Using Epoxy Molding Compositions on Microelectronic Devices

Recent tendencies in the microelectronic device packaging arts seem toenumerate the potential benefits of employing epoxy compounds with lowviscosities. Many modern microelectronic packages employ high pad pitch,high wire density, and long wires. This may be due in part to a trendtoward increased functionality, multiple-die stacking, andpackage-to-package stacking. A potential problem with the increasinglylong wires, and high wire density, is increased potential for wire sweepfailures due to flow of epoxy molding compound. In a representative wiresweep failure, the flow of the molding compound may cause unintendedcontact between two or more proximate wires, causing a short. A lowviscosity epoxy molding composition may tend to reduce the potential forwire sweep.

Additionally, there is a trend in many packages, such as those used inmodern cell phones and other compact electrical devices, toward thinnerform factors. In order to reduce package heights, thinner mold caps areoften employed. The thinner mold caps generally correspond to thinnergaps in the molds. A low viscosity epoxy molding composition may tend toflow through a thinner gap with greater ease.

Still further, in an effort to increase production of packaged devices,many manufacturers have employed larger mold cavities, have increasedthe density of packages in the cavities, and have reduced the mold cycletime. A low viscosity epoxy molding composition may tend to flow throughthe larger molds in a shorter a shorter period of time.

A liquid crystalline epoxy compound and composition as disclosed hereinmay tend to alleviate some of these pervasive problems and greatlyadvance the art of packaging microelectronic devices. In one embodimentof the invention, an epoxy composition as disclosed herein may besolidified over at least a portion of a surface of a semiconductordevice (e.g., a silicon die), or other microelectronic device. A method,according to one embodiment of the invention, may include contacting thesurface of the microelectronic device with the epoxy molding compositionand then solidifying the composition on the surface. The solidifiedcomposition may tend to protect the device from the environment (e.g.,moisture, temperature, contamination), protect the device frommechanical shock, provide structure and support, and/or provideelectrical insulation.

In contacting the surface of the device with the composition, transfermolding, compression molding, or other approaches known in themicroelectronic device packaging arts may optionally be employed. As oneexample, in the case of transfer molding, the microelectronic device maybe introduced into a mold cavity, the epoxy mold compound may be heatedto a temperature greater than its melting point temperature (e.g., atemperature greater than about 150° C.), pressure may be applied to theheated composition to force the composition into the mold cavity, theliquid composition in the cavity may contact the surface of themicroelectronic device, and curing or other polymerization reactions maysolidify the molding composition on the surface of the device. Furtherdetails of one exemplary embodiment of encapsulating a microelectronicdevice using an epoxy molding composition are given in Example 6.

IV. Other Uses of Epoxy Molding Compositions

In another exemplary embodiment of the invention, the epoxy compoundsand compositions disclosed herein may be used to form dielectricsubstrates. Further details of one exemplary embodiment are given inExample 7. In still other embodiments of the invention, the epoxycompounds and compositions disclosed herein may be employed adhesives,plastics, plastic coatings, composite materials, or paints.

V. EXAMPLES Example 1 Synthesizing Exemplary Epoxy Resin Compound

This prophetic example shows how to synthesize a liquid crystallineepoxy monomer compound having the chemical formula:

In a first reaction stage, about 0.5 moles oftrans-1,4-dihydroxycyclohexane and 0.25 moles of p-acetoxybenzoylchloride may be dissolved in about 100 ml of pyridine and stirred atroom temperature for about 6 hrs to encourage reaction. The solution maybe poured onto about 50 g of ice to precipitate the product. The solidmay be filtered, washed with water, and then washed with ethanol. Thesolid material may then be purified by precipitating a concentratedmethylene chloride solution into methanol, and then filtering andwashing the resulting solid. In a second reaction stage, the acetylprotecting group may be removed by stirring the material in an acidifiedsolution of isopropanol and water. In a third reaction stage,epoxidation may be achieved by dissolving about 0.3 moles of thediphenol material and about 0.7 moles of epichlorohydrin into about 100ml of methanol. Then about 25 ml of a 48% aqueous solution of sodiumhydroxide may be added dropwise over about 20 minutes while maintaininga solution temperature of about 30° C. Then the flask may be fitted witha reflux condenser and the solution may be refluxed for about 4 hrs. Thesolution may then be cooled and then neutralized with hydrochloric acid.The methanol may be removed by rotary evaporation. About 200 g of warmwater may be added, and the resulting precipitate may be filtered,washed with water, and then dried in a vacuum oven at about 80° C.overnight. This general procedure may be modified, without undueexperimentation, by those skilled in the art, and having the benefit ofthe present disclosure, in order to synthesize a wide variety of othercompounds, having similar structure.

Example 2 Making Epoxy Resin Compound

This prophetic example shows how to synthesize a liquid crystallineepoxy monomer compound having the chemical formula:

In a first reaction stage, about 0.25 moles oftrans-1,4-cyclohexyldiacetyl chloride and 0.5 moles of p-acetoxyphenolmay be dissolved in about 100 ml of pyridine and stirred at roomtemperature for about 6 hrs. The solution may be poured onto about 50 gof ice to precipitate the product. The solid may be filtered, washedwith water, and then washed with ethanol. The materials may be purifiedby precipitating a concentrated methylene chloride solution intomethanol. Then the resulting powder may be filtered and washed. In asecond reaction stage, the acetyl protecting group may be removed bystirring the material in an acidified solution of isopropanol and water.In a third reaction stage, epoxidation may be achieved by dissolvingabout 0.2 moles of the diphenol material and about 0.7 moles ofepichlorohydrin into about 100 ml of methanol. Then about 25 ml of a 48%aqueous solution of sodium hydroxide may be added dropwise over about 20minutes while maintaining a solution temperature of about 30° C. Thenthe flask may be fitted with a reflux condenser and the solution may berefluxed for about 4 hrs. The solution may then be cooled and thenneutralized with hydrochloric acid. The methanol may be removed byrotorary evaporation. About 200 g of warm water may be added, and theresulting precipitate may be filtered, washed with water, and then driedin a vacuum oven at about 80° C. overnight.

Example 3 Making Epoxy Resin Compound

This prophetic example shows how to synthesize a liquid crystallineepoxy monomer compound having the chemical formula:

In a first reaction stage, about 0.3 moles of trans-stilbenediphenol andabout 0.7 moles of 4-chlorobutyl allyl ether may be mixed with about 100ml of methanol. Then about 25 ml of a 48% aqueous solution of sodiumhydroxide may be. added dropwise over about 20 minutes while maintaininga solution temperature of about 30° C. Then the flask may be fitted witha reflux condenser and the solution may be refluxed for about 4 hrs. Thesolution may then be cooled, and next neutralized with hydrochloricacid. The solution may then be extracted several times with methylenechloride. Then the methylene chloride solutions may be combined, driedover anhydrous magnesium sulfate overnight, filtered and thenevaporated. In a second stage, the resulting material may be epoxidizedby mixing about 0.2 moles of the material with about 0.3. g of anatase(K)—TiO₂ (support) impregnated with hexaammonium heptamolybdate in about100 ml of toluene. Then about 0.5 mmol of tertiary-butyl hydroperoxidein toluene may be added and the mixture may be refluxed for about 6 hrs.The resulting mixture may be filtered, concentrated by evaporation andthen added to about 100-ml of methanol to precipitate the product. Theproduct may be collected by filtration and washing with methanol thenwater, and then dried overnight in a vacuum oven at about 80° C.

Example 4 Making Epoxy Molding Composition

This prophetic example shows how to make an exemplary epoxy moldingcomposition using a liquid crystalline epoxy compound. Any of the epoxycompounds disclosed herein may be employed. In addition to the epoxycompound, other ingredients that may be used include Bisphenol F,silica, carnauba wax, 3,4-epoxypropyl trimethoxy silane, and triphenylphosphine. Initially, about 13.5 g of the epoxy compound, 11.5 g ofBisphenol F, 75 g of silica, 0.3 g of carnauba wax, 0.2 g of3,4-epoxypropyl trimethoxy silane, and 0.15 g of triphenyl phosphine maybe added to a blender equipped with cooling, for example water-cooledgrinding blades, that may be used to help maintain the temperature ofthe material at about 25° C. The ingredients may then be dry-blended.The dry-blended ingredients may be transferred to a roll mill and milledat about 110° C. The heated roll-milling tends to uniformly mix orcompound the materials. The roll-milled material may be ground to aconvenient particle size for pelleting. The ground material may bepressed into a pellet using a press with sufficient pressure to evacuatea majority of the air.

Example 5 Making Epoxy Molding Composition

As another prophetic example, a variation of the epoxy moldingcomposition may be made by combining about 15 g of the epoxy compound,10 g of Bisphenol F, 75 g of silica, 0.3 g of carnauba wax, 0.2 g of3,4-epoxypropyl trimethoxy silane, and 0.15 g of triphenyl phosphine inthe blender and preparing the composition as disclosed in the priorexample.

Example 6 Using Epoxy Resin Composition

This prophetic example shows how to use the epoxy resin compositionaccording to either of the previous two examples to encapsulate amicroelectronic device using transfer molding. A microelectronic device,such as a die and die frame, may be placed into a mold cavity and themold may be closed. A pellet may be placed in a pot at the top of theclosed mold. A member such as a plunger may be placed in the pot abovethe molding composition. The composition may be heated to about 165° C.in order to melt the composition. Pressure may be applied to the plungerto force the melted composition into the cavity. The melted compositionmay flow over and around the exposed surfaces of the microelectronicdevice. The elevated temperatures may cure and solidify the moldingcomposition in the mold. Then, the press may be opened and the moldedmicroelectronic device may be removed from the cavity.

Example 7 Using Epoxy Resin Composition

This prophetic example shows how to use any of the epoxy compoundsdisclosed herein to form a dielectric substrate including a layer ofcured epoxy material. Initially, an epoxy composition may be prepared bycombining starting ingredients in a planetary mixer. The ingredients mayinclude about 210 g methyl ethyl ketone, 60 g of the epoxy compound, 20g of ortho-cresol novolak epoxy resin (215 g/eq), 15 g ofepoxy-terminated polybutadiene rubber, 50 g of brominated phenolicnovolak resin, 4 g of2,4-diamino-6-(2-methyl-1-imadizolyethyl)-1,3,5-triazine-isocyanuricacid adduct, and 11 g of silica with a maximum particle size of 5microns. In general, in forming such dielectric substrates, the silicamay be employed at from about 0 to 40 wt %, or 5 to 15 wt %. Thecombined ingredients may be heated to about 80° C. and may be mixed atabout 50 rpm for about 1 hr. The mixture may be milled by passing themixture twice through a three-roll mill at a temperature of about 80° C.The heated milling may help to mix and compound the ingredients. Themilled material may then be formed as a layer on a 40 μm thick or otherthickness Mylar® brand polyester film. In one aspect, the layer may becast or otherwise applied using approaches such as roll coating, reverseroll coating, gravure roll coating, reverse gravure coating, air knifecoating, tension kiss coating, or variations thereof The layer may befurther formed by drying by heating the applied layer to about 100° C.for about 15 minutes. The dried layer may have a thickness of from about25 to 70 μm. The film and dried layer may be laminated onto a substrateby vacuum lamination at about 120° C. and about 1 torr. In one aspect,the substrate may include a copper plated, fire retardant woven glassreinforced epoxy resin, such as in an FR4 substrate. Often, the copperon the top and bottom surfaces may include etched line and tracepatterns. The layer may be cured at about 170° C. for about 2 hours. Inone aspect, the dielectric substrate may be used as a support formicroelectronic devices.

VI. Other Matters

While the invention has been described in terms of several embodiments,those skilled in the art will recognize that the invention is notlimited to the embodiments described, but may be practiced withmodification and alteration within the spirit and scope of the appendedclaims. The description is thus to be regarded as illustrative insteadof limiting.

In the description above, for the purposes of explanation, numerousspecific details have been set forth in order to provide a thoroughunderstanding of the embodiments of the invention. It will be apparent,however, to one skilled in the art, that other embodiments may bepracticed without some of these specific details. In other, instances,well-known structures, devices, and techniques have been shown in blockdiagram form or without detail in order not to obscure the understandingof this description.

Many of the methods are described in their most basic form, butoperations may be added to or deleted from the methods. It will beapparent to those skilled in the art that many further modifications andadaptations may be made. The particular embodiments are not provided tolimit the invention but to illustrate it. The scope of the invention isnot to be determined by the specific examples provided above but only bythe claims below.

It should also be appreciated that reference throughout thisspecification to “one embodiment” or “an embodiment” means that aparticular feature may be included in the practice of the invention.Similarly, it should be appreciated that in the foregoing description ofexemplary embodiments of the invention, various features are sometimesgrouped together in a single embodiment, Figure, or description thereoffor the purpose of streamlining the disclosure and aiding in theunderstanding of one or more of the various inventive aspects. Thismethod of disclosure, however, is not to be interpreted as reflecting anintention that the claimed invention requires more features than areexpressly recited in each claim. Rather, as the following claimsreflect, inventive aspects lie in less than all features of a singleforegoing disclosed embodiment. Thus, the claims following the DetailedDescription are hereby expressly incorporated into this DetailedDescription, with each claim standing on its own as a separateembodiment of this invention.

In the claims, any element that does not explicitly state “means for”performing a specified function, or “step for” performing a specifiedfunction, is not to be interpreted as a “means” or “step” clause asspecified in 35 U.S.C. Section 112, Paragraph 6. In particular, any useof “step of” in the claims herein is not intended to invoke theprovisions of 35 U.S.C. Section 112, Paragraph 6.

1. A compound comprising: at least one epoxy group; a melting pointtemperature that is less than 140° C.; and liquid crystallinity at atemperature greater than 150° C.
 2. A composition comprising: thecompound of claim 1; and a filler having a coefficient of thermalexpansion that is comparable to that of silicon.
 3. A method comprising:contacting a surface of a microelectronic device with the composition ofclaim 2; and solidifying the composition on the surface.
 4. Amicroelectronic device comprising: a surface; and a compositionsolidified on the surface by the method of claim
 3. 5. The compound ofclaim 1, having the formula:

wherein Ar includes a liquid crystalline moiety selected fromtrans-stilbenediyl, triphenyl, 1,4-bis(phenoxycarbonyl)cyclohexdiyl, anddiphenyl 1,4-cyclohexane-dicarboxylate; X¹ and X² independently of oneanother are selected from oxygen, carbonyl, carboxyl, oxycarbonyl, andamine; and n¹ and n² independently of one another are numbers selectedfrom 4 to
 6. 6. The compound of claim 1, having the formula:

wherein Ar includes a liquid crystalline moiety selected fromtrans-stilbenediyl, triphenyl, 1,4-bis(phenoxycarbonyl)cyclohexdiyl,diphenyl 1,4-cyclohexanedicaroxylate; X¹ and X² independently of oneanother are selected from oxygen, carbonyl, carboxyl, oxycarbonyl, andamine; Y¹ and Y² independently of one another are selected from oxygen,carbonyl, carboxyl, oxycarbonyl, and amine; and n¹ and n² independentlyof one another are numbers selected from 4 to
 6. 7. The compound ofclaim 1, having the formula:

wherein X is selected from a C₆₋₁₀ aryl group and a C₅₋₁₀ alicyclicgroup; each R¹ is independently selected from hydrogen, halogen, andC₁₋₃ alkyl optionally substituted with halogen, provided that not morethan four of the R¹ are C₂ alkyl optionally substituted with halogen,and provided that not more than three of the R¹ are C₃ alkyl optionallysubstituted with halogen; and each R² is independently selected from aC₂₋₆ epoxy.
 8. The compound of claim 1, having the formula:

wherein X is selected from a C₆₋₁₀ aryl group and a C₅₋₁₀ alicyclicgroup; each R¹ is independently selected from hydrogen, halogen, andC₁₋₃ alkyl optionally substituted with halogen, provided that not morethan four of the R¹ are C₂ alkyl optionally substituted with halogen,and provided that not more than three of the R¹ are C₃ alkyl optionallysubstituted with halogen; each R² is independently selected from a C₂₋₆epoxy.
 9. A compound having the formula:

wherein Ar includes a liquid crystalline moiety; X¹ and X² independentlyof one another are selected from oxygen, carbonyl, carboxyl,oxycarbonyl, and amine; n¹ and n² independently of one another arenumbers selected from 2 to
 20. 10. The compound of claim 9, wherein n¹and n² independently of one another are numbers selected from 2 to 10.11. The compound of claim 10, wherein n¹ and n² independently of oneanother are numbers selected from 2 to
 6. 12. The compound of claim 11,wherein n¹ and n² independently of one another are numbers selected from3 to
 5. 13. The compound of claim 9, wherein Ar is selected fromtrans-stilbenediyl, triphenyl, 1,4-bis(phenoxycarbonyl)cyclohexdiyl, anddiphenyl 1,4-cyclohexanedicaroxylate.
 14. The compound of claim 9,comprising a melting point temperature that is less than 140° C., andliquid crystallinity at a temperature greater than 150° C.
 15. Acomposition comprising: the compound of claim 9; and a filler.
 16. Amethod comprising: contacting a surface with the composition of claim15; and solidifying the composition on the surface by polymerizing thecompound.
 17. A microelectronic device comprising: a surface; and acomposition solidified thereon by the method of claim
 16. 18. A compoundhaving the formula:

wherein Ar includes a liquid crystalline moiety; X¹ and X² independentlyof one another are selected from oxygen, carbonyl, carboxyl,oxycarbonyl, and amine; Y¹ and Y² independently of one another areselected from oxygen, carbonyl, carboxyl, oxycarbonyl, and amine; n¹ andn² independently of one another are numbers selected from 2 to
 20. 19.The compound of claim 18, wherein n¹ and n² independently of one anotherare numbers selected from 2 to
 10. 20. The compound of claim 19, whereinn¹ and n² independently of one another are numbers selected from 2 to 6.21. The compound of claim 20, wherein n¹ and n² independently of oneanother are numbers selected from 3 to
 5. 22. The compound of claim 18,wherein Ar is selected from trans-stilbenediyl, triphenyl,1,4-bis(phenoxycarbonyl)cyclohexdiyl, and diphenyl1,4-cyclohexanedicaroxylate.
 23. The compound of claim 18, comprising amelting point temperature that is less than 140° C., and liquidcrystallinity at a temperature greater than 150° C.
 24. A compositioncomprising: the compound of claim 18; and a filler.
 25. A methodcomprising: contacting a surface with the composition of claim 24; andsolidifying the composition on the surface by polymerizing the compound.26. A microelectronic device comprising: a surface; and a compositionsolidified thereon by the method of claim
 25. 27. A compound having theformula:

wherein X is selected from acetylene, vinyl, butadiene, aryl, andalicyclic; each R¹ is independently selected from hydrogen, halogen, andC₁₋₃ alkyl groups optionally substituted with halogen; and each R² isindependently selected from a C₂₋₁₀ epoxy.
 28. The compound of claim 27,wherein the aryl comprises a C₆₋₁₀ aryl group, and wherein the alicycliccomprises a C₅₋₁₀ alicyclic group.
 29. The compound of claim 28, whereinthe aryl group is selected from phenyl and napthyl, and wherein thealicyclic group is selected from cyclopentyl, cyclohexyl, cycloheptyl,cyclooctyl, adamantyl, norbomyl, bicyclo[4.3.0]nonane,bicyclo[3.2.1]octane, and bicyclo[2.2.2]octane.
 30. The compound ofclaim 27, wherein each R¹ is independently selected from hydrogen,halogen, and C₁₋₂ alkyl groups optionally substituted with halogen. 31.The compound of claim 27, wherein not more than four of the R¹ compriseC₂ alkyl optionally substituted with halogen.
 32. The compound of claim31, wherein not more than three of the R¹ comprise C₃ alkyl optionallysubstituted with halogen.
 33. The compound of claim 27, wherein R²comprises a C₂₋₅ epoxy.
 34. The compound of claim 27, comprising amelting point temperature that is less than 140° C., and liquidcrystallinity at a temperature greater than 150° C.
 35. A compositioncomprising: the compound of claim 27; and a filler.
 36. A methodcomprising: contacting a surface with the composition of claim 35; andsolidifying the composition on the surface by polymerizing the compound.37. A microelectronic device comprising: a surface; and a compositionsolidified thereon by the method of claim
 36. 38. A compound having theformula:

wherein X is selected from acetylene, vinyl, butadiene, aryl, andalicyclic; each R¹ is independently selected from hydrogen, halogen, andC₁₋₃ alkyl groups optionally substituted with halogen; and each R² isindependently selected from a C₂₋₁₀ epoxy.
 39. The compound of claim 38,wherein the aryl comprises a C₆₋₁₀ aryl group, and wherein the alicycliccomprises a C₅₋₁₀ alicyclic group.
 40. The compound of claim 39, whereinthe aryl group is selected from phenyl and napthyl, and wherein thealicyclic group is selected from cyclopentyl, cyclohexyl, cycloheptyl,cyclooctyl, adamantyl, norbomyl, bicyclo[4.3.0]nonane,bicyclo[3.2.1]octane, and bicyclo[2.2.2]octane.
 41. The compound ofclaim 38, wherein each R¹ is independently selected from hydrogen,halogen, and C₁₋₂ alkyl groups optionally substituted with halogen. 42.The compound of claim 38, wherein not more than four of the R¹ compriseC₂ alkyl optionally substituted with halogen.
 43. The compound of claim42, wherein not more than three of the R¹ comprise C₃ alkyl optionallysubstituted with halogen.
 44. The compound of claim 38, wherein R²comprises a C₂₋₅ epoxy.
 45. The compound of claim 38, comprising amelting point temperature that is less than 140° C., and liquidcrystallinity at a temperature greater than 150° C.
 46. A compositioncomprising: the compound of claim 38; and a filler.
 47. A methodcomprising: contacting a surface with the composition of claim 46; andsolidifying the composition on the surface by polymerizing the compound.48. A microelectronic device comprising: a surface; and a compositionsolidified thereon by the method of claim 47.